Browsing by Author "Ikeda-Ohno, A"
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- ItemAccumulation of plutonium in mammalian wildlife tissues following dispersal by accidental-release tests(Elsevier, 2016-01-01) Johansen, MP; Child, DP; Caffrey, EA; Harrison, JJ; Hotchkis, MAC; Payne, TE; Ikeda-Ohno, A; Thiruvoth, S; Beresford, NA; Twining, JR; Davis, EWe examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife inhabiting the relatively undisturbed, semi-arid former Taranaki weapons test site, Maralinga, Australia. The accumulation of absorbed Pu was highest in the skeleton (83% ± 6%), followed by muscle (10% ± 9%), liver (6% ± 6%), kidneys (0.6% ± 0.4%), and blood (0.2%). Pu activity concentrations in lung tissues were elevated relative to the body average. Foetal transfer was higher in the wildlife data than in previous laboratory studies. The amount of Pu in the gastrointestinal tract was highly elevated relative to that absorbed within the body, potentially increasing transfer of Pu to wildlife and human consumers that may ingest gastrointestinal tract organs. The Pu distribution in the Maralinga mammalian wildlife generally aligns with previous studies related to environmental exposure (e.g. Pu in humans from worldwide fallout), but contrasts with the partitioning models that have traditionally been used for human worker-protection purposes (approximately equal deposition in bone and liver) which appear to under-predict the skeletal accumulation in environmental exposure conditions. © 2015, Elsevier Ltd.
- ItemAccumulation of plutonium in mammalian wildlife tissues: comparison of recent data with the ICRP distribution models(International Conference on Radioecology and Environmental Radioactivity, 2014-07-01) Johansen, MP; Child, DP; Davis, E; Hotchkis, MAC; Payne, TE; Ikeda-Ohno, A; Twining, JRWe examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife to address the paucity of such data under environmental exposure conditions. Pu activity concentrations were measured in Macropus rufus (red kangaroo), Oryctolagus cuniculus (European rabbit), and Pseudomys hermannsburgensis (sandy inland mouse)inhabiting the relatively undisturbed, semi-arid conditions at the former Taranaki weapons test site at Maralinga, Australia. Of the absorbed Pu (distributed via circulatory and lymph systems) accumulation was foremost in bone (83% ±10% SD), followed by muscle (9% ±10%), liver (7% ±7%), kidneys (0.5% ±0.3%), and heart (0.4% ±0.4%). The bone values are higher than those reported in ICRP 19 and 48 (45-50% bone), while the liver values are lower than ICRP values (30-45% liver). The ICRP values were based on data dominated by relatively soluble forms of Pu, including prepared solutions and single-atom ions produced by decay following the volatilisation of uranium during nuclear detonation (fallout Pu, ICRP 1986). In contrast, the Maralinga data relates to low-soluble forms of Pu used in tests designed to simulate accidental release and dispersal. We measured Pu in lung, GI-tract and the skin and fur as distinct from the absorbed Pu in bone, liver, muscle, and kidneys. Compared with the mean absorbed activity concentrations, the results for lung tissues were higher by up to one order of magnitude, and those in the GI tract contents and the washed skin/fur were higher by more than two orders of magnitude. These elevated levels are consistent with the presence of low-soluble Pu, including particulate forms, which pass through, or adhere upon, certain organs, but are not readily absorbed into the bloodstream. This more transitory Pu can provide dose to the lung and GI tract organs, as well as provide potential transfer of contamination when consumed in predator-prey food chains, or during human foodstuff consumption. For example, activity concentrations in O. cuniculus edible samples prepared according to traditional aboriginal methods were more than two orders of magnitude higher than in muscle alone. The increase was due to inclusion of GI tract components and contents in the traditional method. Our results provide new insights into the sequestration of Pu in mammalian tissues under environmental exposure conditions. These results contrast with those related to the specific forms of Pu and exposure conditions upon which the ICRP models were based. However, they provide data relevant to the assessment of key environmental legacy waste sites, and of potential release scenarios for the low-soluble oxide forms in the growing worldwide inventory of Pu associated with power production.
- ItemAnalysis of hot particle characteristics affecting environmental fate and interaction with living organisms(SPERA, 2016-09-09) Johansen, MP; Child, DP; Collins, RN; Hotchkis, MAC; Howell, NR; Payne, TE; Ikeda-Ohno, A; Mokhber-Shahin, LThe 2nd International Conference on the Sources, Effects and Risks of Ionizing Radiation (SERIR-2) and the 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA-2016) and will be held in Bali, Indonesia 5-9 September 2016. The South Pacific Environmental Radioactivity Association (SPERA), in conjunction with the Indonesian National Nuclear Energy Agency (BATAN) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) made the decision to jointly hold these conferences in one week at the same venue to avoid topical overlap and to strengthen regional participation at both events. SERIR2 will be a 1-day conference (5 September) and deals with the efforts to enhance data collection and disseminate scientific findings related to the issues of sources, effects and risks of the ionizing radiation, as well as to seek ways of communicating with stakeholders (scientific communities, regulatory authorities and general public) on those issues. The 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA), to be held 6-9 September, provides a platform for discussion and debate among scientists on the occurrence, behaviour, impact and measurement of radioactive species present in the environment through natural processes, or resulting from human activities. This international conference facilitates knowledge sharing on environmental radioactivity and related topics of local and global significance. The joint conference will be held 5-9 September 2016, with a welcome reception on 4 September, at the Sanur Paradise Plaza Hotel in Bali. The joint conference will include a one-day workshop on the 6 September on topic(s) to be decided.
- ItemHydrolysis of tetravalent cerium for a simple route to nanocrystalline cerium dioxide: an in situ spectroscopic study of nanocrystal evolution(John Wiley and Sons, 2013-04-29) Ikeda-Ohno, A; Hennig, C; Weiss, S; Yaita, T; Bernhard, GDespite the rapid developments in recent nanocrystal research and their expanding applications, the evolution mechanism of nanocrystals remains veiled for the most part due to the lack of appropriate analytical techniques. Here we demonstrate one promising multi-spectroscopic approach for the in situ investigation of nanocrystal evolution. That is, the formation of nanocrystalline cerium dioxide (NC-CeO2) has been probed by dynamic light scattering (DLS), X-ray absorption spectroscopy (XAS) and high-energy X-ray scattering (HEXS). The obtained results indicate that the fine colloidal particles of NC-CeO2 are formed in an acidic aqueous solution simply through the hydrolysis of the initial precursor of small oligomer CeIV species. This information on how NC-CeO2 evolves is fundamental to simplifying and alleviating the synthetic strategy for NC-CeO2 production. © 2013, Wiley‐Vch Verlag.
- ItemRadioactive particles from a range of past nuclear events: challenges posed by highly varied structure and composition(Elsevier B. V., 2022-10-10) Johansen, MP; Child, DP; Collins, RN; Cook, M; Howell, NR; Ikeda-Ohno, A; Young, ELWhile they have appeared only recently in earth's history, radioactive particles from anthropogenic sources are widespread in global environments and present radiological harm potentials to living organisms. Exposure potentials vary greatly, however few studies examine a wide range of source and particle types. Here we compare a varied set of particles from past nuclear fission and non-fission sources in Australia of highly diverse magnitudes, release modes, and environments. The radiochemistry and microscopy methods revealed that numerous radioactive particles persist in soils 60+ years after their release events. Particles can be distinguished by their Ca/Fe and Si/Fe elemental ratios, which in this study range over orders of magnitude and reflect the materials available during their individual formation events. The particles with Si- and Ca-dominant compositions persisted in corrosive environments (e.g., marine). Internal fracturing is more prevalent than previously reported, and fracturing is greater in Ca-rich vs. Si-dominated matrices. The fractures often form connective pathways from the interior to exterior surfaces, increasing the potential to leach radionuclides into a host organism or the environment. The particles from nuclear testing have dominant 239+240Pu activity concentrations, relative to 90Sr and 137Cs, which increases long-term radiological hazard from alpha emissions if inhaled or ingested, and contrasts with particles from nuclear power accidents (e.g., Fukushima). Additional physical/chemical/radiological measurements are needed to fully understand long-term fate and hazard potentials. Crown Copyright © 2022 Published by Elsevier B.V.
- ItemSolution speciation of plutonium and americium at an Australian legacy radioactive waste disposal site(ACS Publications, 2014-08-15) Ikeda-Ohno, A; Harrison, JJ; Thiruvoth, S; Wilsher, KL; Wong, HKY; Johansen, MP; Waite, TD; Payne, TEDuring the 1960s, radioactive waste containing small amounts of plutonium (Pu) and americium (Am) was disposed in shallow trenches at the Little Forest Burial Ground (LFBG), located near the southern suburbs of Sydney, Australia. Because of periodic saturation and overflowing of the former disposal trenches, Pu and Am have been transferred from the buried wastes into the surrounding surface soils. The presence of readily detected amounts of Pu and Am in the trench waters provides a unique opportunity to study their aqueous speciation under environmentally relevant conditions. This study aims to comprehensively investigate the chemical speciation of Pu and Am in the trench water by combining fluoride coprecipitation, solvent extraction, particle size fractionation, and thermochemical modeling. The predominant oxidation states of dissolved Pu and Am species were found to be Pu(IV) and Am(III), and large proportions of both actinides (Pu, 97.7%; Am, 86.8%) were associated with mobile colloids in the submicron size range. On the basis of this information, possible management options are assessed. © 2014, American Chemical Society.
- ItemSynthesis and characterization of antibacterial silver nanoparticle-impregnated rice husks and rice husk ash(American Chemical Society, 2013-05-09) He, D; Ikeda-Ohno, A; Boland, DD; Waite, TDSilver nanoparticle (AgNP)-impregnated rice husks/rice hush ash (RHs/RHA) were successfully synthesized, and their potential application as antibacterial materials in water disinfection was investigated with particular attention given to the use of both white rice husk ash (WRHA) and black rice husk ash (BRHA) produced by the combustion of RHs as AgNP supports. AgNPs, with diameter of ∼20 nm, were anchored tightly onto RHA, with the emplacement of the AgNPs on these supports increasing the antibacterial activity of the AgNPs through diminution in the extent of nanoparticle aggregation. Ag K-edge XANES analysis revealed that AgNP-impregnated RHs/RHA are composed of both Ag(0) and Ag(I) species with the Ag(I)/Ag(0) ratio following the order WRHA (65:35) > RHs (59:41) > BRHA (7:93). Sodium thioglycolate, a strong Ag(I) ligand, significantly affected the bactericidal activities of AgNP-impregnated RHs/RHA, suggesting that Ag(I) released from AgNP-impregnated RHs/RHA plays an important role in disinfection. The rate constants of oxidative and dissociative dissolution of Ag(0) and Ag(I) species associated with BRHA are 5.0 × 10–4 M–1s–1 and 1.0 × 10–5 s–1, respectively, while those associated with WRHA are 7.0 × 10–2 M–1s–1 and 2.0 × 10–4 s–1 respectively, demonstrating that the rate of dissolution of silver associated with BRHA is particularly slow. As such, the bactericidal “lifetime” of this material is long and exhibits a lower health risk as a result of release of Ag(I) to consumers than does AgNP-impregnated WRHA. © 2013, American Chemical Society.